1. Field
Exemplary embodiments of the present invention relate to a semiconductor design technology, and more particularly, to a semiconductor memory device for preventing the degradation due to word line disturbance, an operating method thereof, and a memory system including the semiconductor memory device.
2. Description of the Related Art
As the degree of integration of a memory increases, a space between word lines included in the memory such as a DRAM is reduced. As the space between the word lines is reduced, a coupling effect between adjacent word lines may increase.
Meanwhile, whenever data is inputted and outputted to or from a memory cell, a word line toggles between an activated state and a deactivated state. Since the coupling effect between adjacent word lines may increase as described above, the data of a memory cell connected with a word line adjacent to a frequently activated word line may be degraded. Such a phenomenon is called word line disturbance or word line hammer. Due to the word line disturbance, the data of a memory cell may be degraded within an expected retention time of the memory cell to be refreshed.
FIG. 1 is a diagram illustrating a part of a cell array included in a DRAM for explaining the word line disturbance.
In FIG. 1, ‘WLL’ corresponds to a frequently activated word line, which has a large number of activation times (or a high activation frequency). Further, ‘WLL−1’ and ‘WLL+1’ correspond to adjacent word lines, which are disposed adjacent to the frequently activated word line WLL. Furthermore, ‘CL’ denotes a memory cell connected to the frequently activated word line WLL, ‘CL−1’ denotes a memory cell connected with the adjacent word line WLL−1, and ‘CL+1’ denotes a memory cell connected with the adjacent word line WLL−1. The memory cells CL, CL−1 and CL+1 include cell transistors TL, TL−1 and TL+1 and cell capacitors CAPL, CAPL−1 and CAPL+1, respectively. For reference, ‘BL’ and ‘BL+1’ denote bit lines.
When the frequently activated word line WLL is activated or deactivated, the voltages of the adjacent word lines WLL−1 and WLL+1 are increased or decreased due to a coupling phenomenon occurring among the word lines WLL, WLL−1 and WLL+1. Accordingly, the amount of charges charged in the cell capacitors CAPL−1 and CAPL+1 is affected, so that the data of the memory cells CL−1 and the CL+1 may be degraded.
Furthermore, as electromagnetic waves, which are generated while the word line toggles between the activated state and the deactivated state, introduce or discharge electrons into or from the cell capacitors of the memory cells connected with adjacent word fines, data are likely to be degraded.